The point is that the boat needs a bit of point to rotate around. When you pull the boards up the force direction is more side ways when the puff is coming in and then you don't have enough grip ( rotate point) to stear the boat down and you are always to slow in accelaration, but when the boat have some grip you are able to stear quick enough, the boat will "rotate" around the board. When you leaf a bit of grip available the boat will not go sideways only it will go forward also and this will give you the possiblity to stear in a puff lower. In A-class we leave ,when doing wildthing, the lower board half in to have grip and the higher board full in the hull, when we put both boards up the wildthing is not going that fast because the sideway motion is to big. When you have more sail (spnaker) to generate more sideway motion the problem is even getting worse.